It's no secret that the Orioles are the worst team in baseball this season. On 24 June they won their 20th game of the year, the last team in baseball to do to (and 20 days after the second to last team). They're in a race with the 1988 Orioles to become the worst team in Orioles history and the 1962 Mets to be the worst team ever. As such, there is only one option for the O's as they approach the trade deadline: sell, sell, sell.
The Orioles will be looking to boost their minor league system with any trades; GM Andy MacPhail has already stated that the O's won't be trading simply to dump salary. Although it has improved in recent years, the Orioles still lack solid positional prospects in the top levels. The only positions at the major league level that are set for the future are catcher, right field, and center field (maybe, if Adam Jones gets his act together), so that leaves things pretty wide open for Andy MacPhail on possible returns.
Starting pitcher Kevin Millwood and infielder Ty Wigginton are the two Orioles most likely to be traded by the deadline. Both are on the last year of their contracts and unlikely to be re-signed by the Orioles. Neither will fetch a top prospect but both could be valuable pieces to contending teams down the stretch. Camden Chat writer James F recently examined teams rumored to be interested in these two players, including the Twins, Cardinals, Rockies, and Mets, and specific players in those systems that would be a good return for the Orioles.
Other players that could be traded, although less likely, are starting pitcher Jeremy Guthrie and LF/1B/DH Luke Scott. Both are under team control for multiple years and are relatively inexpensive, so the Orioles will want more for either of them than Millwood and Wigginton. The Orioles will be looking for multiple minor league prospects or even a major league ready player for either of these two, and will be happy to keep both of them if no other teams offer up value in return.
It's unlikely any other Orioles will be moved this year. The young players are the team's hope for the future and the other veterans (other than Nick Markakis, who is both a young player and a veteran) just aren't performing well enough to pique any interest around the league.